Chapter 3.1-3.3 Flashcards
1
Q
What is the simplest example of nervous system activity?
A
Reflex
2
Q
Receiving info is the _________ function of the NS, carried out by the __________
A
sensory, PNS
3
Q
Processing info is the ____________ function of the NS, carried out by the _______
A
integrative, CNS
4
Q
Acting on info is a _______ function carried out by the _______
A
motor, PNS
5
Q
Describe the muscle stretch reflex
A
Sensory neuron detects stretch, transmits info down its long dendrites and axons to the motor neuron cell body in the spinal chord, motor synapse with muscle stretched to cause contraction
6
Q
Monosynaptic reflex arc
A
Involves 2 neurons and 1 synapse
7
Q
How does quadriceps contract and hamstring relax when patellar tendon is stretched?
muscle stretch reflex
A
Sensory neuron stimulated by stretch, 2 things happen. 1. a motor neuron leading to quadriceps motor neuron is stimulated, causing the quadriceps to contract
2. sensory neuron also synapses with an inhibitory interneuron （ short neuron which forms an inhibitory synapse with motor neuron innervating the hamstring muscle), therefore the hamstring relaxes when the patellar tendon.
8
Q
Give an example of reciprocal inhibition.
A
Concurrent relaxation of the hamstring and contraction of the quadriceps upon stimulation of the sensory neuron.
9
Q
If a reflex occurs without the involvement of the brain, how are we aware of the brain?
A
- Sensory neuron also branches to form a synapse with a neuron leading to the brain. 2. other sensory action is received after the action is taken.
10
Q
Basic functional and structural unit of the nervous system
A
Neuron
11
Q
Bipolar neurons
A
Neurons with one dendrite
12
Q
Multipolar neurons
A
Neurons with multiple dendrites
13
Q
Resting membrane potential
A
Electric potential across the plasma membrane of approximately -70 mV, with the interior of the cell negatively charged with respect to the exterior of the cell.
14
Q
Na+/K+ ATPase
A
Pumps 3Na+ out of the cell and 2K+ in to the cell w/ the hydrolysis of 1 ATP m/c
15
Q
What is the result of Na+/K+ ATPase?
A
A sodium gradient with high Na out of the cell and a K+ gradient with high K+ inside the cell.
16
Q
Leak channels
A
Channels that are open all the time and allow specific ions to leak across the membrane according to their gradient.
17
Q
What is the ratio of K+ leak to Na+ leak
A
100:1 ; membrane is virtually impermeable to sodium
18
Q
Are neurons the only cells with a resting membrane potential?
A
No. All cells have a resting membrane potential. Neurons and muscle tissue are unique in using the membrane potential to generate action potentials.
19
Q
If the K+ leak channels are blocked , what will happen to the membrane potential?
A
Flow of K+ out of the cell makes the cell interior more negatively charged. Blocking K+ leak channels would reduce the magnitude of the resting membrane potential, making the interior of the cell less negative.
20
Q
What would happen to the membrane potential if sodium ions were allowed to flow down their concentration gradient?
A
Sodium ions are positively charged, if they are allowed to flow down the concentration gradient into the cell, making the interior of the cell less negative and even relatively positive is enough ions flow into the cell.
21
Q
Why can cells be described as polarized
A
The resting membrane potential establishes a negative charge along the interior of axons ( along the rest of the neuronal interior), the cells r negative on the inside and positive on the outside.
22
Q
Depolarization
A
Change in the membrane potential frodm the resting membrane potential of approximately -70 mV to less a negative , or even positive potential.
23
Q
Repolarization
A
Returns the membrane potential to normal.
24
Q
What causes the change in membrane potential ?
A
Movement of ions into and out of the neurons through ion channels.
25
What do voltage-gated sodium channels do?
In response to change in membrane potential, ions channels open to allow sodium ions to flow down gradient into the cell and depolarize that section of the membrane.
26
What is the effect of opening the voltage-gated sodium channels on the membrane potential?
Sodium ( positively charged) flows into the cell, down its concentration gradient , making the interior of the cell less negatively charged/ even positively charged.
27
If an action potential starts at one end of an axon , will it run out of energy and not reach the other end of the axon?
No, it cannot. Action potentials are continually renewed at each point in the axon as they travel. Assuming there r enough voltage-gated channels , once an action potential, starts, it will propagate without a change in amplitude (size) until it reaches a synapse.
28
Which can cause the interior of neuron to have a momentary positive charge?
A. Open K+ leak channels
B. Activity of Na+/K+ ATPase
C. Opening of voltage-gated sodium channels
D. Opening of voltage-gated K channels
C. Choices A, B and D all make the interior of the neuron more negatively charged.
29
```
Given the above description, which of the following best describes the response of voltage gated sodium channels to a membrane depolarization from -70mV to -60mV?
A. All of the channels open fully
B. 50% of channels open fully
C. All of the channels open 50%
D. None of the channels open
```
Voltage gated Na channels require threshold depolarization to open. A depolarization below the threshold potential will produce no response, while a depolarization greater than or equal to the threshold will cause all of the channels to open fully. This is called an all or none response. The correct answer is D. The depolarization is less than the threshold , so there is no response.
30
Describe how voltage gated Na channels contribute to repolarizing the membrane potential
1) Voltage gated Na channels inactivate very quickly after they open, shutting off the flow of Na+ into the cell. The channels remain inactivated until the membrane potential nears resting values.
31
If a toxin prevents voltage gated Na+ channels from closing, which of the following will occur?
1. Voltage gated K+ channels will open but not close
2. The membrane will not repolarize to the normal resting membrane potential.
3. The Na+/K+ ATPase will be inactivated.
A) 1 only B) 2 only C) 1 and 2 only D) 2 and 3 only
1 is true. Voltage gated K+ channels are normally closed by the repolarization of the mem so if the mem is not repolarized, they will not close. 2 is true. Na+ ions will continue to flow into the cell even as Na+/K+ ATPase works to pump them out. This will prevent repolarization of the membrane. 3 is false. Na+/K+ ATPase will work harder than ever. Therefore, the answer is C.
32
Myelin
Insulating sheath many neurons are wrapped in
33
Glia cells which create the myelin sheaths in PNS and CNS.
PNS: Schwann cells
CNS: Oligodendrocytes
34
Would an axon be able to conduct action potentials if the entire length was wrapped in myelin?
No. Action potential requires movement of ions across the plasma mem to create a wave of depolarization and no ions can enter or exit a neuron where the axonal membrane is covered with myelin.
35
What is another name for the cell body of a neuron?
Soma
36
What is special about the parts of the axon which are wrapped in myelin?
There is no membrane depolarization and no voltage gated sodium channels in these regions.
37
What are nodes of ranvier?
Periodic gaps in the myelin sheath which allow for the passage of ions to occur. Voltage gated Na+ channels and K+ channels are concentrated in nodes of Ranvier in myelinated axons.
38
What effect does myelin sheath have on the movement of potentials?
Myelin sheath dramatically speeds up the movement of action potentials by forcing action potentials to jump from node to node.
39
Saltatory conduction
rapid jumping conduction in myelinated axon
40
Which one of the following is true concerning myelinated and unmyelinated axons?
A) The amount of E consumed by the Na+/K+ ATPase is much less in myelinated axons than in unmyelinated axons .
B) Myelinated axons can conduct many more action potentials per second than can unmyelinated axons
C) The size of action potential depolarization is much greater in myelinated axons than in unmyelinated axons.
D) Voltage gated potassium channels do not play a role in repolarization in unmyelinated axons
Since the A of mem that is conducting is much less in myelinated axons, Na+/K+ ATPase only works to maintain the resting potential in the nodes of Ranvier , whereas in unmyelinated axons the Na+/K+ ATPase hydrolyzes ATP to maintain the resting potential across the entire membrane.( Choice A is correct) The length of the refractory period ( and hence the frequency of action potentials ) is based on the characteristics of the voltage gated Na and K channels , which do not change (choice B is false). The size of depolarization in an action potential does not vary greatly; action potentials are an all or nothing response ( choice C is false). Voltage gated K channels are same in both neurons (choice D is false).
41
Equilibrium potential
Membrane potential where the driving force ( gradient) does not exist. In other words, there would be no net movement of ions across the membrane.
42
What is the equilibrium potential for Na+ and what does this mean regarding ion movements?
Na+ eq.m potential is positive 50 mV. Na+ are driven inward by the concentration gradient. However, if the inside of the cell is too positive, the positively charged ions are repelled, which means that the electrical gradient would drive sodium out. Both of these forces the chemical gradient driving sodium in and the electrical gradient driving sodium out balance eac other at about +50 mV.
43
Glial cells
Specialized, non-neuronal cells that typically provide structural and metabolic support to neurons. They maintain resting membrane potential but do not generate action potentials.
44
List the location and primary function of
| Schwann cells
Schwann (PNS): form myelin- increase speed of conduction of action potentials along axon
45
What is the equilibrium potential for K+
K+ has a negative equilibrium potential.
46
Nernst Equation and what it is used to do
E= (RT/zF) ln ( X outside/ X inside)
where E is the equilibrium potential for the ion, R is the universal gas constant, T is the temperature in Kelvin, z is the valence of the ion, F is faraday's constant and X is the concentration of the ion on each side of the membrane to create a chemical gradient. The relative concentration of the ion on each side of the membrane create the chemical gradient, while the valence ( charge of the ion) helps determine the electrical gradient. The equilibrium potential for any ion is based on the electrochemical gradient for that ion across the membrane.
47
What is the resting membrane potential and what does this reflect regarding the number of each relative channels?
The resting membrane potential is -70 mV. If the cell was completely permeable for K+, the resting potential would be around -90 mV. The fact that the resting potential is very close to the K+ eq. m potential indicates that there are a large number of K+ leak channels in the membrane; the cell at rest is almost completely permeable to K+. The resting potential is slightly more positive than the resting potential of K+, therefore there are a few Na+ leak channels in the membrane. When the membrane does become completely permeable to Na+ at the beginning of the action potential, the membrane shoots up to +35 mV.
48
What is the effect of the passage of one action potential on the membrane?
The passage of one action potential makes the neuron nonresponsive to membrane depolarization and unable to transmit another action potential or refractory, for a short period of time.
49
Absolute refractory period
During this period, a neuron will not fire another action potential no matter how strong a membrane depolarization is induced.
50
Relative refractory period
During this period, neuron can be induced to transmit an action potential, but the depolarization required is greater than normal because the membrane is hyperpolarized.
51
If a fruit fly mutant is found that it has voltage gated K channels that shut more quickly after repolarization, how would this affect the refractory period in the fly?
The absolute refractory period would not be altered, since this is due to the inability of voltage gated sodium channels to open. However, the relative refractory period would decrease.
52
Describe the functions of the following:
Dendrites
Axon
Axon Terminal
Dendrites: receives signals from neighboring neurons
Axon: transmit signals over a distance
Axon terminal: transmits signals to neuron dendrites and tissues
53
Synapse
Junction between the axon terminus of a neuron and dendrites , soma or axon of a second neuron. It can also be the junction between the axon terminus and an organ
54
Electrical synapses
Occur when the cytoplasms of two cells are joined by gap junctions. When 2 cells are joined by these, an action potential can spread directly from 1 cell to the other. Not common in the nervous system although they are quite important in propagating action potentials in smooth and cardiac muscle.
55
Chemical synapses
Found at ends of axons where they meet their target cells: action potential is converted into a chemical signal.
56
Steps involved in the transmission of a signal across a chemical synapse in the nervous system as well as at the junction of neurons with other cell types, such as skeletal muscle cells.
1. An action potential reached the end of an axon, the synaptic knob
2) Depolarization of the presynaptic membrane opens voltage gated Ca channels
3. Ca influx into the presynaptic cell causes exocytosis of neurotransmitter stored in secretory vesicles.
4. Neurotransmitter molecules diffuses across the narrow synaptic cleft ( small space between cells).
5. Neurotransmitter binds to receptor proteins in the postsynaptic membrane. These receptors are ligand gated ion channels.
6. The opening of these ion channels in the postsynaptic cell alters the membrane polarization.
7. If the membrane depolarization of the postsynaptic cell reaches the threshold of voltage gated sodium channels, an action potentials is initiated.
8. Neurotransmitter in the synaptic cleft is degraded and or removed to terminate the signal.
57
Neuromuscular junction
Chemical synapse that is commonly used
Junction between neurons and skeletal muscle
The neurotransmitter that is released at the neuromuscular junction is acetylcholine. When an action potential reaches a synapse, ACh is released into the synaptic cleft.The ACh binds to its receptor, the receptor opens its associate Na channel, allowing Na to flow down a gradient into the cell, depolarizing the postsynaptic cell membrane. Meanwhile, the ACh in the synaptic cleft is degraded by the enzyme acetylcholinesterase (AChE).
58
A Typical Synapse
| Pre and Post synaptic neuron
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Presynaptic neuron
1. Voltage gated Ca channels open
2. Influx of Ca
3. Exocytosis of secretory vesicle
4. Release of neuro into synaptic cleft
Postsynaptic neuron
1. Neurotransmitter binds to ligand gated ion channels
2. Ions enter postsynaptic cell
3. Membrane polarization is increased or decreased.
```
59
Other neurotransmitters
gamma aminobutryric acid GABA
serotonin
dopamine
norepinephrine
60
Excitatory neurotransmitters
A neurotransmitter which opens a channel and depolarizes the postsynaptic membrane. Example ACh
61
Inhibitory neurotransmitters
Neurotransmitters which induce hyperpolarization of postsynaptic membrane. Hyperpolarization is making the postsynaptic membrane potential more negative than the resting potential.
62
What determines the effect on the postsynaptic cell?
The receptor for the neurotransmitter and its associated ion channel. It is not the neurotransmitter which determines the effect on the postsynaptic cell.
63
Do neurotransmitters have fixed properties as an inhibitory or an excitatory neurotransmitter?
No , the same neuro can be excitatory in some cases and inhibitory in others.
64
If a neuro causes entry of Cl- into the post cell, is the neurotransmitter excitatory or inhibitory?
Chloride ions are negatively charged. The entry of Cl into the cell will make the postsynaptic potential more negative or hyperpolarized, so the neuro is inhibitory.
65
If an inhibitor of acetylcholinesterase is added to a neuromuscular junction, then the post membrane will:
A) be depolarized by action potentials more frequently
B) be depolarized longer with each action potential
C) be resistant to depolarization
D) spontaneously depolarize
B is the correct answer. If AChE is inhibited, ACh remains in the synaptic cleft longer, and ACh gated sodium channels remain open longer with each action potential that reaches the synapse. If the Na channels are open longer, the depolarization of the postsynaptic membrane will last longer.
66
Signals can be sent in only one direction through synapses such as neuromuscular junction. Which of the following best explains unidirectional signaling at synapses between neurons?
A) Neuro is always degraded by postsynaptic cell or in the synaptic cleft
B) Only the pre cell has vesicles of neuro
C) Axons can propagate action potentials in only 1 direction
D) Only the post cell has a resting membrane potential
Signalling is unidirectional because only pre cell has vesicles of neuro that are released in response to action potentials and only post neuron has receptors that bind neuro to either depolarize or hyperpolarize the cell. B is correct. Degradation of neuro is irrelevant to the direction of signal propogation ( A is wrong), axons are capable of propagating action potentials in both directions ( although this is not what they normally do) therefore C is wrong and all cells have a resting membrane potential D is wrong.
67
Does magnitude of depolarization vary from 1 action potential to another?
No
68
What is the key regulated step in the nervous system?
Whether or not the neuron will fire an action potential
69
How are action potentials initiated and is it possible to initiate depolarization as a result of a neurotransmitter by 1 action potential?
Action potentials are initiated when the postsynaptic membrane reaches threshold depolarization ( about -50 mV) required to open voltage gated Na channels . The depolarization caused by the release of a neurotransmitter by 1 action potential is not generally sufficient to induce this degree of depolarization.
70
Summation and decision whether to fire an action potential or not
Decision by post whether to fire an action potential or not can be determined by adding effect of all synapses impinging on neuron, both excitatory and inhibitory.
Summation is the addition of stimuli
71
Excitatory postsynaptic potentials
| Inhibitory postsynaptic potentials
EPSPs otherwise known as postsynaptic depolarization are caused by excitatory neuro
IPSPs are caused by inhibitory neuro
72
Temporal Summation
Occurs when the pre neuron fires so rapidly that the EPSPs or IPSPs add up on top of each other. If they are EPSPs, the additive effect might be enough to reach the threshold depolarization required to start a postsynaptic action potential. If they r IPSPs, the postsynaptic cell may hyperpolarize, moving further and further away from the threshold as it become inhibited. Temporal summation talks about the additive effect of EPSPs which are generated from 1 synapse by a series of high frequency action potentials on the presynaptic neuron.
73
Spatial summation
EPSPs or IPSPs from all synapses on he post are summed at any given moment in time. If the total of the sum causes the post to reach the threshold voltage, the action potential will be fired. Spatial summation is the additive effect which is created by many EPSPs which have been generated at many different synapses on the same post neuron at the same time.
74
In which of the following ways can a presynaptic neuron increase the intensity of the signal it transmits?
A) Increase the size of presynaptic action potentials
B) Increase the frequency of action potentials
C) Change type of neuro it transmits
D) Change speed of action potential propogation
A neuron cannot change the size of action potentials it transmits, but it can increase the number of action potentials it transmits in a given amount of time ( the frequency of action potentials ) . The increase frequency of action potentials can add up thru temporal sum in the post cell to produce an increased response ( B is the answer). Action potentials are all or nothing once they r started. The magnitude of mem depolarization during propogation of the action potential does not change . A is wrong, A neuron cannot change the type of neuro it releases, C is wrong; and the speed of propogation cannot be varied from 1 action potential to the next D is wrong .
75
Somatic division of PNS
Portion of system concerned with conscious sensation and deliberate voluntary movement of skeletal muscle.
76
Autonomic division of PNS
Portion concerned with digestion, metabolism, circulation, perspiration and other involuntary processes.
77
2 efferent portions of autonomic division
Sympa and parasympa
78
General effects of sympa and para
When sympa activated, body is prepared for fight or flight; results in the release of epinephrine into the bloodstream by the adrenal medulla
When para activated , body prepared to rest and digest
79
Para and sympa effect on digestive system: glands
para: stimulation
sympa: inhibition
80
Para and sympa on digestive system: motility
para: stimulation ( stimulates digestion)
sympa: inhibition ( inhibits digestion)
81
Para and sympa on digestive system: sphincters
para: relaxation
sympa: contraction
82
Para and sympa on urinary system bladder
P: contraction ( stimulates urination)
S: relaxation (inhibits urination)
83
P and S on urinary system: urethral sphincter
P: relaxation ( stimulates urination)
S: contraction ( inhibits urination)
84
P and S on bronchial smooth muscle
P: constriction ( closes airways)
S: relaxation ( opens airways)
85
P and S on cardio system: heart rate and contractility
P: decreased
S: increased
86
P and S on cardio system: blood flow to skeletal muscle
P: -
S: increased
87
P and S on skin
P: -
S: sweating and general vasoconstriction; emotional vasodilation ( blushing)
88
P and S on eye: pupil
P: constriction
S: dilation
89
P and S on eye: muscle controlling lens
P: near vision accommodation
S: accommodation for far vision
90
P and S on adrenal medulla
P: No effect
| S; Release of epinephrine
91
P and S on genitals
P: erection/lubrication
S: ejaculation/ orgasm
92
reflex
response to a stimulus which does not require the involvement of conciousness
93
components of a reflex
1. afferent ( involves info about a stimulus into the CNS)
| 2. efferent ( carries info away from the CNS to initiate a response in the periphery
94
reflexes and side of the body the efferent goes to
some like the muscle stretch has afferent which brings info in from 1 side of the body and efferent which brings info to that same side
others efferent comes on both sides
95
descrbe how voltage gated potassium channels contribute to repolarization of the membrane
2) Voltage-gated K+ channels open more slowly than the voltage gated Na+ channels and stay open longer
Voltage gated K+ channels open in response to membrane depolarization. As the K+ leaves the cell dn its conc.n gradient , mem pot.l returns to negative values , actually overshooting the resting potential by about 20 mV to about -90 mV . At this pt, K+ channels close.
96
describe how Na+/K+ pump contributes to the repolarization of the membrane
3) K+ leak channels and Na+/K+ ATPase continue to function ( as they always do) to bring the mem back to resting potential. It could do so alone but it would take a lot longer.
97
name the three factors which contribute to repolarization of the membrane
Na+ voltage gated
K+ voltage gated
Na+/K+ pump
98
list location and primary function of
| Oligodendrocytes
Oligodendrocytes (CNS): form myelin- increase speed of conduction of action potentials along axon
99
list location and primary function of
| Astrocytes
Astrocytes ( CNS): Guide neuronal development, regulate synaptic communication via regulation of neurotransmitter levels
100
list location and primary fuction of
| Microglia
Microglia (CNS): Remove dead cells and debris
101
list location and primary function of
| Ependymal cells
Ependymal cells (CNS): Produce and circulate cerebrospinal fluid
102
Ehat does the equlibrium potential of K+ regarding ion movement
K+ are driven outward by their concentration gradient. However, if the interior of the cell is too negative, the positively charged ions cannot escape the attraction ; the electrical gradient drive K+ in. The chemical gradient driving K+ out and the electrical gradient driving K+ in balance each other at about -90 mV, so this is the equilibrium potential for K+.
103
voltage gated Na+ during absolute refractory period
During this time, the voltage gated Na channels have been inactivated after depolarization. They will not be able to open again until the membrane potential reaches the resting potential and the Na channels have reached their closed state. These periods help direct the action potential because only channels further downstream can open and let in the depolarizing ions.
104
hyperpolarized period during relative refractory period
Hyperpolarized state is found in the brief period in which the membrane potential is more negative than the resting potential as a result of the voltage gated K channels which have not closed yet. Because it is further from the threshold, a greater stimulus is required to open the voltage gated Na channels to start an action potential.
105
relative refractory period is the period after
absolute refractory period when it is really hard to send an action potential. It would take more positive ions than usual to reach appropriate depolarization potential. The initial triggering event would have to be bigger than normal to send more action potentials along.
